Rotary actuator

ABSTRACT

A rotary actuator has a stator having plural permanent magnets  1   a  and  1   b;  a rotor having a rotor core  3  which plural salient poles  3   a  and  3   b  are formed at, and one or more rotor coils  5  are wound around; an electromagnetic torque generating portion A comprising the stator and the rotor which, by supplying an electric current to the rotor coils  5,  generates an electromagnetic torque which displaces a relative angle position of the rotor and the stator in approximate proportion to the magnitude of the electric current; and a coil spring  36  biased in approximate proportion to the magnitude of the relative angle displacement of the rotor and the stator, and thereby generating a torque in the direction opposite to the direction of the electromagnetic torque. When the exciting current is supplied to the rotor coils  5,  the electromagnetic torque in approximate proportion to the magnitude of the electric current is generated between the rotor and the stator, which makes the coil springs 36 bias and the rotor or the stator rotate to and be held at the angular position where the generated electromagnetic torque corresponds to the opposite torque generated by the coil spring  36.

TECHNICAL FIELD

This invention relates to a rotary actuator which is equipped with astator and a rotor, the stator having two permanent magnets, and therotor having a rotor core which two salient poles are formed at and oneor more rotor coils are wound around. The relative angle position of therotor and the stator thereof is displaced by supplying an electriccurrent to the rotor coils.

BACKGROUND INFORMATION

Conventionally, for example, the amount of air sucked into an engine iscontrolled by adjusting the angular aperture of a butterfly valvemounted on a throttle body, which is executed by the switching drive ofa DC motor. In the case, the butterfly valve on the throttle body isdriven by the output torque of the DC motor, which is amplified byeleven times using a double reduction mechanism with two sets of gears,and the angular aperture of the valve is sensed using a potential angledetector composed of a thin film resistor and a set of metal brushes.However, in the case that a DC motor is used as a driver, a backlashresulted from the gears is inevitable, so that the angular aperture ofthe valve is difficult to be accurately controlled. Moreover, thedetrimental effect on the durability, the lifetime, and the accuracycaused by the slide of the metal brushes on the surface of the thin filmresistor is also inevitable in the potential angle detector.

On the other hand, to use rotary actuators, which require no gearscausing a backlash, for rotation control is considered. For example, inJapanese Unexamined Patent Application No. Hei 9-163708, a rotaryactuator is proposed in which a stator coil is wound around a statorcore having two magnetic poles as a stator, a cylindrical rotor isprovided around the stator, and two permanent magnets are secured on theinternal surface of the rotor so as to face the above stator core. Inthis conventional technique, the thickness of both end portions of eachmagnet is set to be not more than 90 percent of that of the centralportion. By controlling the thickness of the permanent magnets in thismanner, the rotor can be reliably rotated only to two target positionswithout generating the opposite torque during supplying no electriccurrent.

In the rotary actuator by the above conventional technology, the rotorstops at an initial position when not supplying an electric current, androtates to a predetermined angular position when supplying an electriccurrent, and returns to the initial position by the torque of thepermanent magnets when the supply of an electric current is stopped. Dueto this, the rotor cannot be stopped and held at any position apart fromabove two angular positions. Therefore, it is impossible to control theangular aperture of the valve for adjusting the above amount of the airsucked into the engine using the rotary actuator by the aboveconventional technology.

DISCLOSURE OF THE INVENTION

The present invention was made in consideration of the above problems,and an object of the present invention is to provide a rotary actuatorwith a simple structure of which the rotor and the stator can bedisplaced to a predetermined relative angle position in accordance withthe magnitude and the conducting direction of exciting current.

The present invention provides a rotary actuator including: a statorhaving plural permanent magnets; a rotor having a rotor core whichplural salient poles are formed at, and one or more rotor coils arewound around; an electromagnetic torque generating portion comprisingthe stator and the rotor which, by supplying an electric current to therotor coils, generates an electro-magnetic torque between the stator andthe rotor which displaces a relative angle position of the rotor and thestator in approximate proportion to the electric current; and an elasticmember biased in approximate proportion to the amount of the relativeangle displacement of the rotor and the stator, and thereby generating atorque in the direction opposite to the direction of theelectro-magnetic torque.

In the above structured rotary actuator, when an exciting current issupplied to the rotor coils, an electromagnetic torque in approximateproportion to the current is generated between the rotor and the stator,which makes a relative angle displacement between the rotor and thestator. As a result, the elastic member is biased and the rotor or thestator is stopped and held at an angular position at which the generatedelectro-magnetic torque corresponds to the repulsive torque (oppositetorque) resulted from the bias of the elastic member. Therefore, sincethe relative angle displacement between the rotor and the stator isproportional to the magnitude of the exciting current, an arbitraryangle displacement of the rotor or the stator can be controlled byadjusting the magnitude and the direction of the exciting current, withsuch a simple structure that has no gears, etc., which may be used invarious mechanical devices. In the present invention, although the terms“rotor” and “stator” are used, either the rotor or the stator can bearbitrarily fixed or rotated in the application of this invention.

In the above structured rotary actuator, when the direction of thesupplied electric current is opposite to that of the above current, theelectromagnetic torque in the opposite direction can be generated. Inorder to control the angular positioning of the opposite direction inaddition, the actuator desirably includes: a first elastic member towhich electro-magnetic torque is applied when the rotor or the statorrotates in one rotation direction; and a second elastic member to whichelectromagnetic torque is applied when the rotor or the stator rotatesin the other rotation direction.

In the above case, if the first elastic member and the second elasticmember have elastic moduli different from each other, the relative angleposition of the rotor and the stator displaced by the exciting currentswith the same magnitude but in different directions are different, sothat the present invention can be widely applied.

The angular positioning in both directions can be realized by using asingle coil spring as an elastic member. In this case, the actuator mayinclude a first elastic member driving device rotating together with therotor or the stator when the rotor or the stator rotates in onedirection and thereby biasing the elastic member; and a second elasticmember driving device rotating together with the rotor or the statorwhen the rotor or the stator rotates in the other direction therebybiasing the elastic member. With this feature, the rotor can bias (forexample, compress) the coil spring when rotates in either direction.

Moreover, if applying a preload on the elastic member to bias itbeforehand, the backlash between parts due to manufacture errors andassembly errors can be eliminated when the rotor starts rotating.

The electromagnetic torque generating portion desirably has twopermanent magnets in the stator, and two salient poles formed at therotor core; wherein the permanent, in the circumferential direction, hastwo end portions and one center portion, the radial thickness of the endportion being from 90% to 95% of that of the center portion, thedistance from the radial outline of the center portion of the salientpole to the rotation center of the rotor core is not more than 99% ofthat from the radial outline of the circumferential end portion of thesalient pole to the rotation center of the rotor core, and the anglebetween the line connecting one of circumferential outlines of a salientpole and the rotation center of the rotor core and that connecting theother circumferential outline of the same salient pole and the rotationcenter of the rotor core is not less than 100 degrees.

In the above structured electromagnetic torque generating portion, thegenerated electromagnetic torque is constant within an angulardisplacement range of more than 90 degrees of the rotor at a constantexciting current supplied to the rotor coils, and the magnitude of theelectromagnetic torque is in proportion to the magnitude of the excitingcurrent. When the exciting current is supplied in a direction oppositeto the above, the direction of the electromagnetic torque is opposite,so that the rotor and the stator can be displaced to an arbitrary angleposition within the range in accordance with the magnitude and thedirection of the exciting current with a simple structure.

Following feature can be shown as a concrete structure such that theelectro-magnetic torque is constant within an angular displacement rangeof more than 90 degrees of the rotor at a constant exciting currentsupplied to the rotor coils.

The rotary actuator can be structured such that the radial thickness ofthe circumferential end portion of the permanent magnet is smaller thanthat of the circumferential center portion of the permanent magnet; thedistance from the radial outline of the circumferential center portionof the salient pole to the rotation center of the rotor core is smallerthan that from the radial outline of the circumferential end portion ofthe salient pole to the rotation center of the rotor core; and the anglebetween the line connecting one of circumferential outlines of a salientpole and the rotation center of the rotor core and that connecting theother circumferential outline of the same salient pole and the rotationcenter of the rotor core is an obtuse angle.

Alternatively, the rotary actuator may be structured such that the rotorcore and the permanent magnet have facing surfaces facing each other,and the facing surfaces of the rotor core and the permanent magnet areformed in the shapes of circular arc surfaces of which center positionsare different from each other. The rotary actuator may be structuredsuch that the permanent magnet has a facing surface facing the rotorcore, and the facing surface is formed in the shape of an ellipticalsurface. The rotary actuator may be structured such that the permanentmagnet has a facing surface facing the rotor core and has twocircumferential end portions, and the facing surface at thecircumferential end portion is formed in the shape of a flat-cutsurface.

Also, the rotary actuator may be structured such that the rotor core hastwo facing surfaces respectively facing the two permanent magnets, andeach of the facing surfaces of the rotor core is formed in the shape ofa plurality of circular arc surfaces of which center positions aredifferent from each other. The rotary actuator may be structured suchthat the permanent magnet has end portions in the circumferentialdirection, each of which has a non-magnetized region formed thereat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal-section view showing a structure of a rotaryactuator according to the First Embodiment of the present invention.

FIG. 2 is a cross-section view in the direction indicated by the arrowA-A in FIG. 1.

FIG. 3 is a cross-section view showing a structure of a rotary actuatoraccording to the First Embodiment.

FIG. 4 is a cross-section view showing a stator in which the rotorrotates across 90 degrees from the state shown in FIG. 3 by supplying anexciting current to the rotor coils.

FIG. 5A is a plan view showing a structure of a rotor core, and FIG. 5Bis a plan view showing a structure of a permanent magnet.

FIG. 6 is a graph showing one example of the relationship between theangular position of a rotor and the electro-magnetic torque in the casein which the magnitude of exciting current varies.

FIG. 7 is a cross-section view showing the rotation of a rotor.

FIG. 8A to FIG. 8C are views showing a spring ring; FIG. 8A is a rearside view thereof, FIG. 8B is a longitudinal-section view thereof, andFIG. 8C is a front side view thereof.

FIG. 9A and FIG. 9B are views showing a spring driving ring; FIG. 9A isa longitudinal-section view thereof, and FIG. 9B is a front side viewthereof.

FIG. 10 is a graph showing one example of the relationship among theangular position of a rotor, the electro-magnetic torque and theopposite torque produced by a coil spring in the case in which themagnitude of exciting current varies in the First Embodiment.

FIG. 11 is a longitudinal-section view showing a structure of a rotaryactuator according to the Second Embodiment of the present invention.

FIG. 12 is a cross-section view in the direction indicated by the arrowA-A in FIG. 11.

FIG. 13 is a graph showing one example of the relationship among theangular position of a rotor, the electro-magnetic torque, and theopposite torque produced by a coil spring in the case in which themagnitude of exciting current varies in the Second Embodiment.

FIG. 14 is a longitudinal-section view showing a structure of a rotaryactuator according to the Third Embodiment of the present invention.

FIG. 15 is a cross-section view in the direction indicated by the arrowA-A in FIG. 14.

FIG. 16A to FIG. 16C are views showing a peripheral spring ring; FIG.16A is a rear side view thereof, FIG. 16B is a longitudinal-section viewthereof, and FIG. 16C is a front side view thereof.

FIG. 17A to FIG. 17B are views showing an inner spring ring; FIG. 17A isa longitudinal-section view thereof, and FIG. 17B is a front side viewthereof.

FIG. 18A to FIG. 18C are views showing a spring driving ring; FIG. 18Ais a front side view thereof, FIG. 18B is a longitudinal-section viewthereof, and FIG. 18C is a rear side view thereof.

FIG. 19 is a graph showing one example of the relationship among theangular position of a rotor, the electromagnetic torque, and theopposite torque produced by coil springs in the case in which themagnitude of exciting current varies in the Third Embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. First Embodiment A.Structure of First Embodiment

The First Embodiment of the invention will hereinafter be explained withreference to FIG. 1 to FIG. 10. FIG. 1 is a longitudinal-section viewshowing a rotary actuator according to the First Embodiment of thepresent invention. This rotary actuator schematically has anelectromagnetic torque generating portion A and an opposite torquegenerating portion B. First, the structure of the electro-magnetictorque generating portion A will be explained.

In the Figures, reference numerals 1 a and 1 b denote two permanentmagnets secured on the inner surface of a yoke 2 which is a stator. Thepermanent magnet 1 a has a north magnetic pole on the inside thereof anda south magnetic pole on the outside thereof (on the side facing theyoke 2). The permanent magnet 1 b has a south magnetic pole on theinside thereof and a north magnetic pole on the outside thereof (on theside facing the yoke 2). A rotor core 3 has salient poles 3 a, and arotor coil 5 is wound between the salient poles 3 a. A rotor shaft 4 isprovided at the center of the rotor core 3. The above yoke 2 is securedon a holder 6 and a location holder 8. Bearings 7 a and 7 b, whichrotatably hold the rotor shaft 4 penetrating the holder 6 and thelocation holder 8, are provided on the holder 6 and the location holder8.

FIG. 4 shows a state in which an exciting current is supplied to therotor coil 5, and the rotor core 3 rotates across 90 degrees.

FIG. 5A is a plan view showing a structure of the rotor core, and FIG.5B is a plan view showing a structure of the permanent magnet. As shownin FIG. 5A, the salient poles 3 a formed at the rotor core 3 havecircular arcs 3 b having radii R3 at circumferential center portion andcircular arcs 3 f having radii R4 at circumferential end portions. Thatis, the facing surfaces of the salient poles 3 a which face thepermanent magnets 1 a and 1 b are formed in the shapes of circular arcsamong which the radii of the circular arcs 3 b and 3 f are differentfrom each other, and a distance G exists between the center positions ofthe circular arcs having the radii R3 and R4. Specifically, the distancefrom the radial outline of the circumferential center portion of thesalient poles 3 a to the rotation center of the rotor core 3 is not morethan 99% of that from the radial outline of the circumferential endportion of the salient pole to the rotation center of the rotor core 3.

As shown in FIG. 5B, each of permanent magnets 1 a and 1 b has a facingsurface facing the rotor which is formed by a circular arc having aradius R1, and an opposite surface facing the yoke 2 which is alsoformed by a circular arc having a radius R2. Between the arc centers ofthe facing surface and the opposite surface there exists a distance E,which makes the radial thickness B of each circumferential end portionof the permanent magnet be from 90% to 95% of the radial thickness A ofthe circumferential center portion of the permanent magnet.

Next, a structure of the opposite torque generating portion B will beexplained.

As shown in FIG. 1, a cylindrical spring housing 39 is mounted by bolts20 on a surface of the holder 6. A spring securing plate 38 is fixedbetween the spring housing 39 and the holder 6 so as to be preventedfrom relatively rotating. A spring ring 31 is rotatably supported by therotor shaft 4 inside the spring housing 39.

Protrusions 31 a are formed at one side of the spring ring 31 shown inFIG. 8A to FIG. 8C, which are spaced 180 degrees apart from each other,and a hole 31 b penetrates through one of the protrusions 31 a. Betweenthe spring ring 31 and the spring securing plate 38 there is a spacewhere a coil spring (elastic member) 36 is mounted. One end of the coilspring 36 is inserted in the hole 31 b of the spring ring 31, and theother end thereof is inserted in the hole (not shown in the Figures)formed at the spring securing plate 38.

Two stoppers 30 a and 30 b adjacent to the spring ring 31 are fixedinside the spring housing 39, and spaced 180 degrees apart from eachother. The stoppers 30 a and 30 b are fitted into dovetail grooves 39 aformed on the inner surface of the spring housing 39. As shown in FIG.2, the spring ring 31 is rotatable from the state in which theprotrusion 31 a goes away from the stopper 30 a to the state in whichthe protrusion 31 a contacts the other stopper 30 b. With the rotationthereof, the spring ring 31 compresses the coil spring 36.

A spring driving ring 35 is mounted on the rotor shaft 4 so as to beadjacent to the spring ring 31. In the Figure, reference numeral 34denotes a key, which prevents from the relative rotation of the rotorshaft 4 and the spring driving ring 35. Two protrusions 35 a protrudingin the radial direction are formed at the peripheral portion of thespring driving ring 35, and spaced 180 degrees apart from each other.Since the outside diameters between the protrusions 35 a are smallerthan the inside diameter between the stoppers 30 a and 30 b, the springdriving ring 35 is rotatable without being held by the stoppers 30 a and30 b. Since the rotation locus of the protrusion 35 a overlaps with thatof the protrusion 31 a of the spring ring 31, when the rotor shaft 4brings the spring driving ring 35 to rotate together, the protrusion 35a of the spring driving ring 35 contacts and pushes the protrusion 31 aof the spring ring 31. As a result, the spring ring 31 is driven torotate together, and the coil spring 36 is thereby compressed.

In FIG. 1, reference numeral 32 denotes a cover, and the cover 32 ismounted to the spring housing 39 by a bolt 33 screwed to the rotor shaft4. The cover 32 prevents from the removal of stoppers 30 a and 30 b.

B. Action of First Embodiment

An action of the above structure of the rotary actuator will beexplained hereinafter.

FIG. 6 is a curve diagram showing one example of the relationshipbetween the angular position of a rotor and the electro-magnetic torquewhen the magnitude of an exciting current varies. As shown in FIG. 6, itis confirmed that the electromagnetic torque is constant within anangular displacement range of the rotor core 3, which is not less than90 degrees at a constant exciting current, and the magnitude of theelectro-magnetic torque is in proportion to that of the exciting current(Hereinafter, the angular displacement range is simply referred to as a“proportional range”). It is confirmed that when the exciting current isapplied in the opposite direction, the electromagnetic torque isgenerated in the opposite direction.

In the above torque generation portion A, the radial thicknesses ofpermanent magnets 1 a and 1 b at the circumferential end portions arefrom 90% to 95% of the radial thicknesses of the circumferential centerportions; the distance from the radial outline of the center portion ofthe salient poles 3 a to the rotation center of the rotor core 3 are notmore than 99% of that from the radial outline of the circumferential endportions of the salient pole 3 a to the rotation center of the rotorcore 3; and the angle between the line connecting one of circumferentialoutlines of a salient pole 3 a and the rotation center of the rotor core3 and that connecting the other circumferential outline thereof and therotation center of the rotor core 3 is not less than 100 degrees.Therefore, when an exciting current is supplied to the rotor coil 5, themagnitude and the direction of the electromagnetic torque generated bythe exciting current are in accordance with that of the exciting currentwithin the proportional range of the rotor core 3, which is not lessthan 90 degrees. When no exciting current is supplied to the rotor coil5, the torque by the permanent magnets 1 a and 1 b is 0 within the aboveproportional range.

FIG. 7 shows the states in which the rotor core 3 rotates by 20 degreeswithin a rotation range from “0 degree”, at which no exciting current issupplied, to “180 degrees” by supplying exciting current. As describedabove, the electromagnetic torque of the rotor core 3 is proportional tothe magnitude of the exciting current within the proportional range,which is not less than 90 degrees. Therefore, if the rotor coil isexcited by a properly chosen current, the rotor core 3 can be rotated toand held at a freely selected angular position within the proportionalrange not less than 90 degrees by the opposite torque generated by theopposite torque generating portion B, and the rotor core 3 can bereturned to an initial angular position by the opposite torque if thesupply of exciting current is stopped.

As shown in FIG. 10, in the First Embodiment, the magnitude of theelectro-magnetic torque is approximately constant corresponding to thatof the exciting current within the angular range from “40 degrees” to“130 degrees”, that is, within the angular range of 90 degrees. Theinitial angle position of the rotor core is set at the stroke of “130degrees” in FIG. 10, which corresponds to the state that the protrusions31 a of the spring ring 31 contact the stoppers 30 a and 30 b in FIG. 2.When the exciting current is supplied to the coil 5, the rotor core 3rotates away from the position shown in FIG. 2 toward counterclockwisedirection. As shown in FIG. 10, a preload is applied to the coil spring36 in above initial state, and the opposite torque generated by the coilspring due to the preload approximately equals the electromagnetictorque generated by the exciting current of 0.15 A supplied to the coil5.

When the supplied exciting current is more than 0.15 A, theelectro-magnetic torque generated between the rotor and the statorincreases, so that the rotor rotates. The rotation of the rotor istransmitted to the spring ring 31 via the rotor shaft 4 and the springdriving ring 35, the spring ring 31 compresses the coil spring 36, andthe opposite torque generated by the coil spring 36 increases along withthe increase of the angular displacement of the rotor, so that the rotorstops and is held at an angular position where the electromagnetictorque is balanced by the opposite torque generated by the coil spring36. In FIG. 10, the opposite torque generated by the coil spring 36 withrespect to the angular displacement (stroke) is indicated using astraight line, and intersection points of this line and theelectromagnetic torque curves are the angular positions where the rotorstops and is held at exciting current 0.30 A, 0.45 A, 0.60 A,respectively. For example, when the exciting current is 0.60 A, therotor rotates across 90 (=130-40) degrees.

In the above structured rotary actuator, when an exciting current issupplied to the rotor coil, the electromagnetic torque approximatelyproportional to the exciting current is generated between the rotor andthe stator, which biases the coil spring 36, and the rotor stopsrotating at an angular position at which the generated electromagnetictorque corresponds to the opposite torque generated by the coil spring36. Therefore, the angular displacement of the rotor is approximatelyproportional to the magnitude of the supplied current, so that angulardisplacement control in various kinds of mechanical devices can beperformed. In the case that this rotary actuator is applied to a valveof a throttle body, the valve can be directly driven, no reductionmechanism is needed, and the angular aperture of the valve can becontrolled with high accuracy since it is proportional to the magnitudeof the exciting current. For the same reason, a sensing mechanism forsensing the angular aperture of a valve, which has problems indurability, lifetime, and accuracy, is not required too. Since no brushis needed, the durability and the lifetime can be improved. Since noreduction gear mechanism is required, the cost reduction and thereliability can be improved. High electromagnetic torque can be obtainedat a low exciting current, and a long period driving can be performed ata high electro-magnetic torque. Since inexpensive magnetic material suchas ferrite magnet can be used for the permanent magnet, the costreduction is possible.

2. Second Embodiment

The Second Embodiment of the present invention will be explained withreference to FIG. 11 to FIG. 13. In a rotary actuator of the SecondEmbodiment, two spring rings 31 shown in FIG. 8A to FIG. 8C and twospring driving rings 35 shown in FIG. 9A to FIG. 9B are used, so thatboth rotation directions of a rotor can be controlled. Since thecomponents of the Second Embodiment are the same as that of the FirstEmbodiment, explanation of the components will be omitted, only theassembled state of the components will be explained.

As shown in FIG. 11, in the Second Embodiment, two stoppers 30 a and 30b are fixed between the holder 6 and the spring housing 39, instead ofthe spring securing plate 38 of the First Embodiment thereat, and twospring driving rings 35 are fixed on the rotor shaft 4 by the keys 34inside the internal sides of two pairs of the stoppers 30 a and 30 b,respectively. Two spring rings 31 are rotatably supported by the rotorshaft 4 next to the spring driving rings 35, so that the rotation locusof the protrusions 31 a thereof overlaps with that of the stoppers 30 aand 30 b. The spring rings 31 and spring driving rings 35 are disposedin the same manner as the First Embodiment. Between the two spring rings31 there is a space where a coil spring 36 is mounted, and two ends ofthe coil spring 36 are respectively inserted into the holes 31 b of thespring rings 31.

As shown in FIG. 12, at the original position, the protrusions 31 a ofthe spring ring 31 on the front side are disposed next to one pair ofthe stoppers 30 a and 30 b on their counterclockwise direction sides,and the protrusions 31 a of the other spring ring 31 on the rear sideare disposed next to the other pair of the stoppers 30 a and 30 b ontheir clockwise direction sides.

When the rotor coil 5 is excited by a current, the rotor rotates towardcounterclockwise direction in FIG. 12, and it drives the spring drivingring 35 and the spring ring 31 on the front side to rotate togethertoward the same direction. Although the torque generated in this case istransmitted to the coil spring 36, the spring ring 31 on the rear sidedoes not rotate since its protrusions 31 a are stopped by the stoppers30 a and 30 b on the rear side. Therefore, the coil spring 36 iscompressed by the rotation of the spring ring 31 on the front side.

As shown in FIG. 13, the rotor rotates from the angular position of 105degrees, where is the original position of the rotor in this case,toward the angular position of 40 degrees. In this Figure, thecharacteristics of the coil spring with respect to the stroke are shownusing solid lines when it is preloaded, and that are shown using dashlines when it is not preloaded. When the rotor rotates towards the abovedirection, the coil spring 36 is rotated and compressed in thecounterclockwise direction viewed from the front side.

When the supply of the exciting current is stopped, the electromagnetictorque between the rotor and the stator disappears, and the rotor ispushed back to the original position by the opposite torque of the coilspring 36. If the direction of the above exciting current is reversed,the electromagnetic torque with the direction opposite to the abovedirection thereof will be generated, so that the rotor rotates towardclockwise direction in FIG. 12, and drives the spring driving ring 35and the spring ring 31 on the rear side to rotate together towardclockwise direction, while the spring ring 31 on the front side isstopped by the stoppers 30 a and 30 b on the front side.

In this case, if a preload is applied to the coil spring 36, the rotorstarts rotating after the exciting current exceeds 0.15 A, and theangular displacement of the rotor is proportional to the magnitude ofthe exciting current.

The same actions and effects as that of the First Embodiment can beobtained from the Second Embodiment. Besides, the feature that theangular positioning in either direction can be controlled makes thiskind of rotary actuator be more widely applicable.

3. Third Embodiment

The Third Embodiment of the present invention will be explained withreference to FIG. 14 to FIG. 19. This rotary actuator is different fromthe First Embodiment in that two coil springs with different springconstants are employed.

As shown in FIG. 14, in the same manner as the First Embodiment, thespring securing plate 38 is fixed between the spring housing 39 and theholder 6 so as to be prevented from the relative rotation. An innerspring ring 12 is rotatably supported by the rotor shaft 4 inside thespring housing 39. The protrusions 12 a are formed at one side of theinner spring ring 12 shown in FIG. 17A and FIG. 17B, and spaced 180degrees apart from each other. A hole 12 b penetrates through one of theprotrusions 12 a. The inner spring ring 12 is disposed so as to bespaced from a spring securing plate 38. An inner coil spring (elasticmember) 11 is mounted between the inner spring ring 12 and the springsecuring plate 38. One end of the inner coil spring 11 is inserted inthe hole 12 b, and the other end thereof is inserted in the hole (notshown in the Figures) formed at the spring securing plate 38.

A peripheral spring ring 18 rotatably rides on the inner spring ring 12.Protrusions 18 a are formed at one side of the peripheral spring ring 18shown in FIG. 16A to FIG. 16C, and spaced 180 degrees apart from eachother. A hole 18 b penetrates through one of the protrusions 18 a. Aperipheral coil spring (elastic member) 10 is mounted between theperipheral spring ring 18 and the spring securing plate 38. One end ofthe peripheral coil spring 10 is inserted in the hole 18 b of theperipheral spring ring 18, and the other end thereof is inserted in thehole (not shown in the Figures) formed at the spring securing plate 38.

Two stoppers 17 a and 17 b adjacent to the inner spring ring 12 and theperipheral spring ring 18 are disposed inside the spring housing 39, andspaced 180 degrees apart from each other. The stoppers 17 a and 17 b arefitted into dovetail grooves 39 a formed on the inner surface of thespring housing 39. As shown in FIG. 15, the protrusions 12 a of theinner spring ring 12 are disposed next to the stoppers 17 a and 17 b onthe counterclockwise direction sides, and the protrusions 18 a of theperipheral spring ring 18 are disposed next to the stoppers 17 a and 17b on the clockwise direction sides. The protrusions 18 a protrude acrossthe stoppers 17 a and 17 b in the axial direction.

A spring driving ring 13 is mounted at the front of the rotor shaft 4.As shown in FIG. 18A to FIG. 18C, two internal protrusions 13 aprotruding in the axial direction are formed at the end face of thespring driving ring 13, and spaced 180 degrees apart from each other.Two peripheral protrusions 13 b protruding in radial direction areformed at the peripheral portion of the spring driving ring 13, andspaced 180 degrees apart from each other. This spring driving ring 13 isfixed on the rotor shaft 4 by the key 34 such that the internalprotrusions 13 a are directed toward the inside. In the state shown inFIG. 15, which is viewed from the direction indicated by the arrow A-Ain FIG. 14, the internal protrusions 13 a are adjacent to theprotrusions 12 a of the inner spring ring 12 on the clockwise directionsides, and the peripheral protrusions 13 b are adjacent to theprotrusions 18 a of the peripheral spring ring 18 on thecounterclockwise direction sides.

In FIG. 15, when an exciting current is supplied to the rotor coil 5,the rotor rotates in clockwise direction, and when the exciting currentwith the direction opposite to that of the above current is supplied tothe rotor coil 5, the rotor rotates in counterclockwise direction. Withregard to the structure in FIG. 15, when the rotor shaft 4 rotates inclockwise direction, the peripheral protrusions 13 b of the springdriving ring 13 push the protrusions 18 a and bring the peripheralspring ring 18 to rotate together, so that the peripheral coil spring 10is compressed. When the rotor shaft 4 rotates in counterclockwisedirection, the internal protrusions 13 a of the spring driving ring 13push the protrusions 12 a and bring the inner spring ring 12 to rotatetogether, so that the inner coil spring 11 is compressed.

As shown in FIG. 19, the original position of the rotor is at theangular position of 120 degrees, and the rotor rotates from the originalposition to the angular position of 45 degrees. In this Figure, thecharacteristics of the inner coil spring 11 and the peripheral coilspring 10 with respect to the stroke are shown using solid lines whenthey are preloaded, and that are shown using dash lines when they arenot preloaded. When the rotor rotates in the counterclockwise direction,inner coil spring 11 is rotated and compressed in the same direction,viewed from the front side.

When the supply of the exciting current to rotor coil 5 is stopped, theelectro-magnetic torque between the rotor and the stator disappears, andthe rotor returns to the original position by the opposite torque of theinner coil spring 11. When the exciting current is supplied in adirection opposite to that of the above current, the electro-magnetictorque with the direction opposite to that of the above electromagnetictorque is generated between the rotor and the stator. In FIG. 15, whenthe rotor rotates in clockwise direction, it drives the spring drivingring 13 and the periphery spring ring 18 to rotate together toward thesame direction, while the inner spring ring 12 is stopped by thestoppers 17 a and 17 b, so that the peripheral coil spring 10 is rotatedand compressed.

Since the spring constant of the peripheral coil spring 10 is largerthan that of the inner coil spring 11, as shown in FIG. 19, the angulardisplacement of the rotor is smaller in comparison with the above casein which the exciting current having the same magnitude is supplied inthe opposite direction. Therefore, the control accuracy of this rotaryactuator can be changed depending on the rotation direction.

In the above embodiments, in order to make the radial thickness B of thecircumferential end portion of each permanent magnet be smaller than theradial thickness A of the circumferential center portion thereof, thefacing surface of each permanent magnet facing the rotor core 3 and theopposite surface facing the yoke 2 are formed in the shapes of circulararc surfaces having center positions different from each other. Insteadof this, the facing surfaces of the permanent magnets 1 a and 1 b facingthe rotor core 3 may be formed in the shapes of elliptical surfaces. Thefacing surfaces of the permanent magnets 1 a and 1 b at thecircumferential end portions, which face the rotor core 3, may be formedin the shapes of flat-cut surfaces. Non-magnetic regions may be formedat the circumferential end portions of the permanent magnets 1 a and 1b. In this case, the same effects as the case in which the thickness isgradually reduced can be obtained.

In the above embodiments, in order to make the distances from the radialoutline of the circumferential center portion of the salient pole 3 a tothe rotation center of the rotor core 3 be smaller than that from theradial outline of the circumferential end portions of the salient pole 3a to the rotation center of the rotor core 3, the facing surfaces of therotor core 3, which face the permanent magnets 1 a and 1 b, are formedin the shapes of circular arc surfaces having the center positionsdifferent from each other. Instead of this, the facing surfaces of therotor core 3, which face the permanent magnets 1 a and 1 b, may beformed in the shapes of elliptical surfaces. The facing surfaces of thesalient poles of the rotor core 3 at the circumferential end portions,which face the permanent magnets 1 a and 1 b, may be formed in theshapes of flat-cut surfaces.

Although the rotor rotates with respect to the stator in the aboveembodiments, the present invention can be applied either to a structurein which the stator rotates with respect to the fixed rotor or to thestructure in which the rotor and the stator are relatively rotated.

The rotary actuator of the present invention can be applied not only tovalves, such as throttle body valves, pressure control valves,proportional bypass valves, but also to various fields, such asperipheral devices for driving a drive of a computer, automatic paymentmachines, control of laser beam deviation, direction control ofparabolic antennas of man-made satellites, direction control of solarpower generators, control of automatic tracking apparatuses of cameras.

1. A rotary actuator comprising: a stator having plural permanentmagnets; a rotor having a rotor core which two salient poles are formedat, and one or more rotor coils are wound around; an electromagnetictorque generating portion comprising the stator and the rotor betweenwhich electromagnetic torque is generated by supplying an electriccurrent to the rotor coils, which, in approximate proportion to themagnitude of the electric current, displaces a relative angle positionof the rotor and the stator; and an elastic member biased in approximateproportion to the magnitude of the relative angle displacement of therotor and the stator and thereby generating a torque in the directionopposite to the direction of the electromagnetic torque.
 2. A rotaryactuator according to claim 1, the actuator further comprising: anelastic member driving device rotating together with the rotor or thestator when the rotor or the stator rotates in a predetermined rotationdirection and thereby biasing the elastic member.
 3. A rotary actuatoraccording to claim 1, the actuator further comprising: a first elasticmember driving device rotating together with the rotor or the statorwhen the rotor or the stator rotates in one direction and therebybiasing an elastic member; and a second elastic member driving devicerotating together with the rotor or the stator when the rotor or thestator rotates in the other direction and thereby biasing the sameelastic member.
 4. A rotary actuator according to claim 1, the actuatorfurther comprising: a first elastic member to which electromagnetictorque is applied when the rotor or the stator rotates in one rotationdirection; and a second elastic member to which electromagnetic torqueis applied when the rotor or the stator rotates in the other rotationdirection.
 5. A rotary actuator according to claim 4, wherein the firstelastic member and the second elastic member have elastic modulidifferent from each other.
 6. A rotary actuator according to claim 1,wherein the elastic member is biased beforehand by applying a preload tothe elastic member.
 7. A rotary actuator according to claim 1, whereinthe actuator is structured such that: the stator having two permanentmagnets; the rotor core having two salient poles; the permanent magnethaving two circumferential end portions and one circumferential centerportion, the radial thickness of the circumferential end portion beingfrom 90% to 95% of the radial thickness of the circumferential centerportion; the distance from the radial outline of the circumferentialcenter portion of the salient pole to the rotation center of the rotorcore being not more than 99% of the distance from the radial outline ofthe circumferential end portion of the salient pole to the rotationcenter of the rotor core; and the angle between the line connecting oneof circumferential outlines of a salient pole and the rotation center ofthe rotor core and the line connecting the other circumferential outlineof the same salient pole and the rotation center of the rotor core beingnot less than 100 degrees.
 8. A rotary actuator according to claim 1,wherein the actuator is structured such that: the permanent magnethaving two circumferential end portions and one circumferential centerportion, the radial thickness of the permanent magnet at thecircumferential end portions being smaller than the radial thickness ofthe permanent magnet at the circumferential center portion, the distancefrom the radial outline of the circumferential center portion of thesalient pole to the rotation center of the rotor core being smaller thanthe distance from the radial outline of the circumferential end portionsof the salient pole to the rotation center of the rotor core, and theangle between the line connecting one of circumferential outlines of asalient pole and the rotation center of the rotor core and the lineconnecting the other circumferential outline of the same salient poleand the rotation center of the rotor core being an obtuse angle.
 9. Arotary actuator according to claim 1, wherein the rotor core and thepermanent magnet have facing surfaces facing each other, the facingsurfaces of the rotor core and the permanent magnet formed in the shapesof circular arc surfaces of which center positions are different fromeach other.
 10. A rotary actuator according to claim 1, wherein thepermanent magnet has a facing surface facing the rotor core, the facingsurface formed in the shape of an elliptical surface.
 11. A rotaryactuator according to claim 1, wherein the permanent magnet has a facingsurface facing the rotor core and has two circumferential end portions,the facing surface at the circumferential end portion formed in theshape of a flat-cut surface.
 12. A rotary actuator according to claim 1,wherein the rotor core has two facing surfaces respectively facing thetwo permanent magnets, each of the facing surfaces of the rotor coreformed in the shape of a plurality of circular arc surfaces of whichcenter positions are different from each other.
 13. A rotary actuatoraccording to claim 1, wherein the rotor core has two facing surfacesrespectively facing the permanent magnets, each of the facing surfacesformed in the shape of an elliptical surface.
 14. A rotary actuatoraccording to claim 1, wherein the rotor core has two facing surfacesrespectively facing the two permanent magnets, the facing surface at acircumferential end portion of the salient pole formed in the shape of aflat-cut surface.
 15. A rotary actuator according to claim 1, whereinthe permanent magnet has two circumferential end portions, each of whichhas a non-magnetized region formed thereat